Do you use artificial light? That can cause a chicken not to go through a full molt.

Chickens will molt one complete and three partial molts during its growth to point of lay. Generally, complete molting occurs from 1-6 weeks of age, and partial molting at 7-9 weeks, 12-16 weeks and 20-22 weeks. During this final molt, the stiff tail feathers grow.
When they are 16-18 months of age they will start their annual molt.

I don't use any artificial light in the coop. I remember when they were young they were growing out their larger feathers, just didn't know this was a type of molt. As for being older and molting, hasn't happened yet. I have about 50 chickens. More than half of them (RR Bard Rock, Cochin) are over two years old with no molting.